THE Earth Summit of 180 nations opened in Rio yesterday with messages of hope from world leaders, tempered by a warning that new barriers were being erected to insulate the more affluent and privileged from the poor.

Maurice Strong, secretary-general of the summit , warned: 'No place on the planet could remain an island of affluence in a sea of misery. We are either going to save the whole world or no one will be saved.

'One part of the world cannot live in an orgy of unrestrained consumption where the rest destroys its environment just to survive. No one is immune from the effects of the other.'

Mr Strong's speech reflected anxieties that the summit has much to negotiate before it can be counted a success.

The United States, in particular, faces heavy pressure to be more positive. But, in their first briefing yesterday, US delegates repeated that they would not sign the convention on bio-diversity.

William Reilly, administrator of the US Environmental Protection Agency, said there was no prospect of the US signing in the near future. Its main priority was better management and conservation of forests, and a convention on saving them.

Britain has yet to announce if it will sign the bio-diversity convention, but is expected to do so today. Although the Government has doubts about the size of the financial commitment, the political gesture to sign is regarded as vital to distance Britain from Washington, although John Major will meet President Bush at Camp David this weekend.

Efforts were being made behind the scenes yesterday to limit the damage done by the US decision. Countries like Malaysia are threatening to refuse to sign the other main convention, on climate change, in retaliation.

There are also fears that other agreements may be under threat. Israel, for example, wants a phrase about 'people under occupation' deleted from the Rio Declaration which all heads of government are expected to sign. It was thought that this document had been finalised, but Israel fears this phrase could be used as a weapon by the Palestinians.

Mr Strong reminded the conference about population pressures - not being discussed because of objections from the Vatican and Third World nations. 'Population must be stabilised, and rapidly,' he said. 'If we do not do it, nature will, and much more brutally. We have been the most successful species ever. We are now a species out of control.

'To continue along this pathway could lead to the end of our civilisation. We have to face up to the dire implications of the warnings scientists are sounding. They point to the prospect that this planet may soon become uninhabitable for people.'

He said rich countries must provide more money, cancel Third World debt, and allow free trade so the south could earn money to develop. 'Like it or not, from here on in, we are in this together rich, poor, north, south. The industrialised world cannot escape its primary responsibility to lead the way in establishing this partnership and making it work.'

Fernando Collor, the Brazilian president and president of the conference, opened the summit with a plea to the rich nations. 'On behalf of all those still forced to live with poverty, we can and we must ask from the rich countries a greater proof of brotherhood. Without a global order with greater justice, there will be tranquil prosperity for no one.'

The UN secretary-general, Boutros Boutros-Ghali, said people could continue to waste the planet's resources for a few more decades. 'But ultimately if we do nothing, then the storm will break on the heads of future generations. For them it will be too late.'